1. Field of the Invention
The present invention is in the field of manufacturing electrical multilayer capacitors and is specifically directed to an improved contact layer for connection to the metallic thin films of the multilayer capacitors, the layer consisting of a combination of aluminum, nickel, and palladium layers.
2. Description of the Prior Art
There is a method described in the prior art for the manufacture of electrical plasma-polymer multilayer capacitors wherein regenerable thin metal layers, preferably composed of aluminum, serve as electrodes and dielectric layers produced by radiation polymerization are alternated with the layers of aluminum and deposited on a carrier material. The electrodes are then freed of oxide layers by sputter etching in the regions intended for contacting the metallic contact layers, and finally, such contact layers are applied to two opposite end faces of the carrier material, partially overlapping the electrodes.
Such a method is disclosed in earlier German Patent Application No. P 34 39 688.8. This application described a composition for contact layers consisting of a structure having a chromium-nickel base layer, a copper intermediate layer, and a covering layer of palladium, palladium-silver, or tin, or a layer sequence having an aluminum base layer and a cover layer of the above-mentioned metals without an intermediate layer.
The aluminum-palladium sequence of layers, however, shows a definite long-term deficiency in the dielectric loss factor. Above this, these layer sequences must be resistant to flow solder for chip application of the capacitor. With the aforementioned metals, however, this requires correspondingly thick metal layers in order to prevent a complete degeneration. For example, the three-layer sequence usually measures about 1.7 microns, and the two-layer sequence about 1.3 microns.
By way of additional background, reference is invited to UK Published Patent Application No. 2 106 714 which describes a ceramic capacitor containing alternate layers of ceramic dielectric material and electrode layers interposed therebetween. Alternate electrode layers have edge portions extending to and exposed at the margins of the capacitor. The margins are coated with a sputter deposited metallic layer which is bonded to the exposed ceramic components of the margins and to the exposed portions of the electrode layers to thereby provide the two terminals. The exposed electrode edges on a given margin are electrically interconnected and the components of the margins are mechanically bonded. The metallic layer may be of nickel or nickel-vanadium alloy and may include a plurality of sub-layers such as chromium, nickel, or silver each applied by sputter deposition.
U.S Pat. No. 3,476,531 describes a circuit contact for wave soldering of metallic leads to thin film resistors. The circuit contact disclosed consists of a copper layer upon which palladium is deposited so that oxidation of the copper is precluded. The amount of palladium present is such that all of the palladium goes into solid solution upon the subsequent application of solder to attach a wire lead to the contact. The contact has a base layer consisting of an 80-20 nickel-chromium alloy, a layer of copper over the base layer, and a layer of palladium on the copper layer.
For further background material, reference is invited to European Published Patent Application No. 0 041 679 and to German OS No. 25 13 509.